1. Technical Field
The present invention relates to a butt welding apparatus for and a butt welding method of melting and jointing a butt portion where end surfaces of two welding sheet members are butted to each other with electric resistance heat generated by power applied between a pair of two electrode members, and to a butt welded product manufactured by the butt welding method.
2. Background Art
FIG. 21 shows a conventional butt welding apparatus. Two welding sheet members 101, 102 having the same thickness are set to the welding apparatus with end surfaces 101A, 102A butted to each other. Each of electrode rollers 103, 104 disposed on both the front and back surface sides of the sheet members 101, 102 has a thickness bridging across the sheet members 101, 102, and power is applied between the electrode rollers 103, 104 when the sheet members 101, 102 are welded. When the power is applied between the electrode rollers 103, 104 while they press both the sheet members 101, 102, the metal material of the sheet members 101, 102 is melted and a nugget 105 is formed in the sheet members 101, 102 at a central portion in the thickness thereof where an electric resistance is increased in the sheet members 101, 102 by the resistance heat of the power flowing in the thickness direction of both the sheet members 101, 102. Further, since the power also flows through a path passing through a butt portion 106 where the end surfaces 101A, 102A are butted to each other, the butt portion 106 is also melted at a central portion in the thickness thereof by the heat generated by the contact resistance of these end surfaces 101A, 102A. Thus, the nugget 105 is formed so as to bridge across both the sheet members 101, 102.
Then, when the electrode rollers 103, 104 move along the butt portion 106 while rolling or when the sheet members 101, 102 move with respect to the electrode rollers 103, 104 that are free to move at a definite position, the nugget 105, which can joint the sheet members 101, 102 with a large amount of strength, is formed over the entire length of the butt portion 106.
To form the nugget 105 bridging across both the sheet members 101, 102, an electrically conductive state must be secured by causing the end surface 101A of the sheet member 101 to be butted to come into contact with the end surface 102A of the sheet member 102. Thus, conventionally, both the end surfaces 101A, 102A are polished over the entire lengths thereof prior to butt welding so as to secure a contact state of the end surfaces 101A, 102A in the butt welding.
Therefore, conventionally, welding sheet members, for example, sheared in predetermined sizes by a shearing apparatus cannot be butt welded in a sheared state and must be subjected to finish processing to the end surfaces 101A, 102A prior to a welding operation, which increases a working cost and a working time.
An object of the present invention is to provide a butt welding apparatus and a butt welding method capable of eliminating processing such as polishing, and the like for finishing the end surfaces of two welding sheet members to be butted prior to butt welding, and to provide a butt welded product capable of being manufactured by the butt welding method.